new sim and new number

Cell C!!! My mobile device was ****** on 15 August 2018. I called Cell C to inform of same. I did not action an immediate sim swap as my account was in arrears. Presently my Cell C account is up to date. I called yesterday 15 October 2018 to reactivate my service etc as I am paying for my subscriptions and i have not been using the services. I told the call centre agent i want to change my number and i was told the costs is R250. I have a new Cell C sim card which the new number must be activated on which I hope can be done...I pray I did explain myself well...the lady did state that since I chose my own digits for the number, back office support will call me back to confirm etc? Now I want to know how are they going to get hold of me?? I do not have a cell c number since 15 August 2018.....and how long does this process take please? you want the monies so deliver the prompt service. Thank you